TraviZ

when tuning a vehicle, such as getting the most spark and fuel out of it without detonation, is this also good for fuel economy? or is their a different way to go at it to get the fuel milage and performance?

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SBC, Forged internals, 215cc aluminum heads, 90mm TB, .600+ lift cam, Long tube headers, 3.5" exhaust. 9" Procharger. Powered by megasquirt 2

Fast355

Keep the engine vacuum as high as possible, while maintaining sharp throttle response, getting away with the least amount of fuel and timing possible.

TraviZ

so for economy, i want to remove spark and fuel?

if i do too much will i also, see detonation?

Fast355

You want to run the least amount of fuel possible, without sacrificing response or causing a lean surge. You COULD see detonation by removing fuel, but you should be able to feel the need for more fuel, before you get to that point.

Your engine may very well want more timing than it does now, due to the leaner A/F mixture. What I mean by the minimum, is run as little timing possible to have good response, good part throttle power, etc.

I guess what I am saying is that if 48* gives the same response and power as 42*, you are actually hurting MPG beingat 48* over 42*

TraviZ

should i start with removing fueling or spark first?

and do u think its an idea to have the lower rpms set for economy, and above a certain rpm, change it for performance?

Fast355

I would pull a little fuel at cruise, read the plugs, then advance your timing a little, read the plugs, then go at it a little more.

TOO LEAN + TOO MUCH TIMING=MELTDOWN

Your best bet is to work off of MAP and TPS, not RPM. I can run 2,500+ rpm in 3rd gear with a light load or I can run 3,000+ WOT. Its not an RPM thing, but rather an engine load thing.

TraviZ

hmm this is starting to cofnuse me. lol i guess i understand that i need to pull fueling. but to add timing?

Fast355

When you run leaner air/fuel mixtures, the burn time increases, necessitating that you light the mixture off sooner. That means that you will need more timing. The trick is too keep the added timing to a minimum.

Grumpy

You want to slightly lean things down, and add some timing. lean mixtures take longer to burn, so they need more timing.

You also need to watch the coolant temp., oil temp is even better for seeing if you're adding too much heat into the system, via being lean, and advancing the timing.

Detonation?, not so much in cruise, unless you really miss the tune. BUT, you can easily get to having tip-in preignition. Remember the K/S is deaf to preignition.

So while you might run alot of timing, in the light load areas, you want to ramp it out quickly, as you get into the higher loads. That and Burst knock retard is your friend.

TraviZ

think maybe i can leave fueling alone then in the cruise areas like stock, and only adjust fueling in the top end? and max my timing out throughout the whole rpm range without detonation?

Fast355

I think you are missing my point on keeping the timing advance set as retarded as possible for good response/power.

MAXING the timing out is not benificial and should be avoided. While you may not be encountering detonation, you are putting NEGATIVE work on the crank by lighting off the mixture too early.

MBT

TraviZ

im sorry im not quite understanding what your trying to say? from a stock timing map, should I be taking out timing for milage?

Fast355

It will more than likely end up being more advanced at low loads than it is now. You just want the minimum amount of timing that you can add, to be added. For example, if it is responsive, in lean cruise with 44* of timing, you don't need to go to 48*

TraviZ

so what if i were to leave it where its at and it runs fine? should i just pull some fuel out as long as i still feel that it runs fine and doesnt hesitate or studder?

Fast355

Yes, as it starts to feel lame, you might try adding just a touch of timing.

You will find that your combo likes about 44-48* of timing and about 15.5:1 a/f ratio at lower maps.

TraviZ

so pull fuel till it feels 'lame' (lol) then add timing to make it feel good again?

Fast355

But be careful, too little fuel+too much timing=meltdown

TraviZ

how can i tell when im going too far?

Fast355

Reading the plugs


Here is an example, don't use as your own, if you do, I am not responsible for what happens!!!

Attached Images

highway mode.jpg (55.6 KB, 113 views)

TraviZ

hehe thanks, i kinda understand, a lil different though since im using maf.